JPH0577465B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an electrostatic precipitator, and more specifically, an electrostatic precipitator of a pulse charging type in which a DC base voltage and a pulse voltage are applied in a superimposed manner. The present invention relates to a charge control method for an electrostatic precipitator.

Prior Art Conventional electrostatic precipitators have been controlled to apply a high voltage within a range that does not cause excessive sparks. Among these, the pulse charging method, which can dramatically improve the performance of dust collectors by instantaneously applying high voltage, has been attracting attention in recent years.

As shown in FIG. 1, this pulse charging method is a method in which a DC voltage (referred to as base voltage) and a pulse voltage are applied in a superimposed manner to an electrostatic precipitator. This pulse charging method consists of a base voltage, a pulse voltage, a pulse frequency f (however, 1/f=T (pulse repetition period))
Since these three types can be controlled independently, it is possible to collect various types of dust such as dust with high electrical resistance.

However, even with the pulse charging method, it is necessary to control the base voltage, pulse voltage, and pulse frequency so as not to generate excessive sparks.

The purpose of controlling spark generation to prevent it from becoming excessive is to maintain dust collection performance as high as possible. When a spark occurs, if you make a mistake in controlling which of the base voltage, pulse voltage, and pulse frequency should be controlled, the dust collection performance will deteriorate.

The inventor of the present invention conducted various studies in order to find optimal values for base voltage, pulse voltage, and pulse frequency to achieve the best dust collection performance.

Research results show that the most important factor determining dust collection performance in pulsed charging is the peak voltage of the pulse. The higher the peak voltage, the better the dust collection performance. On the other hand, if the peak voltage is kept constant, the higher the base voltage and pulse frequency, the better the dust collection performance will be.

However, when both the base voltage and the pulse frequency exceed a certain value, sparks tend to occur suddenly, making it impossible to maintain a high peak voltage. This is because reverse ionization occurs in the dust layer on the surface of the dust collector. Back ionization takes the form of a corona called a back corona when the peak voltage is low, as in the case of DC charging without superimposed pulses, but when the peak voltage is high, as in pulse charging,
Be sure to move to Spark.

Therefore, it is impossible to obtain a high peak voltage with a base voltage or pulse frequency that causes reverse ionization. In summary, in order to obtain high dust collection performance, a high peak voltage is required, and in order to obtain this high peak voltage, a base voltage and pulse frequency that are as low as possible without causing reverse ionization are required.

Therefore, when considering the generation of sparks in the pulse charging method by focusing on the relationship between the peak voltage and the base voltage, the peak voltage at which sparks are generated decreases rapidly when the base voltage exceeds a certain value. In particular, the electrical resistance of the collected dust is 10 ₁₁
This phenomenon is remarkable above Ω·cm.

When collecting dust with such high electrical resistance,
This marginal base voltage is the corona onset voltage in DC charging or only slightly higher. At base voltages lower than the corona initiation voltage, the corona current is almost zero or completely zero, and there is little possibility that reverse ionization will occur due to the base voltage. Further, when the voltage becomes higher than the corona starting voltage to a certain extent, reverse ionization occurs at least locally in the dust collector.
This is because the corona current locally has a fairly large current density. In addition, in the pulse charging method, if the base voltage is below the corona starting voltage limit, back ionization and sparks will not occur. Even if the pulse frequency is too high, back ionization will occur, but at least the base voltage It is possible to prevent excessive voltage from causing reverse ionization.

In conclusion, the optimal value for the base voltage is just slightly above the corona initiation voltage for DC charging. However, even if sparks occur, as long as the frequency is small, there is no need to suppress the base voltage to an unnecessarily low level.

On the other hand, since pulse charging itself has not yet been widely and generally adopted, there are few published documents regarding the control method for sparks caused by pulse charging. For example, in JP-A-57-127462, the timing of spark generation is divided into several types and controlled differently depending on whether it is "during pulse voltage application" or "during base voltage application between pulses". .

However, the method disclosed in JP-A-57-127462 could not achieve sufficient dust collection efficiency.

Problems to be Solved by the Invention Therefore, the present invention aims to provide a pulse voltage control method for a pulse charging type electrostatic precipitator that can realize maximum dust collection efficiency.

Means for Solving Problems According to the feature of the present invention, in an electrostatic precipitator to which a DC base voltage and a pulse voltage are applied in a superimposed manner, when no spark is generated in the precipitator, the pulse voltage is applied at regular intervals. , increase one of the pulse frequencies little by little, and when a spark occurs, if the spark occurs after the pulse voltage increases, decrease the pulse voltage,
In addition, if the spark occurs after the pulse frequency has increased, the pulse voltage is lowered and the pulse frequency is decreased by a width greater than the pulse frequency increase width, and if no spark occurs thereafter, at regular intervals, first, the pulse where the previous spark occurred is Increase the pulse voltage step by step until the voltage is just below the voltage, then increase the pulse frequency step by step. If no spark occurs in the dust collector during that time, continue to increase the pulse voltage and pulse frequency at regular intervals. Charging control of a pulse charging type electrostatic precipitator, characterized in that either one is raised little by little, and on the other hand, when a spark is generated in the precipitator during that time, the above-mentioned operation at the time of spark generation is performed at the time when the spark is generated. A method is provided.

In addition, in the above method, if there is no spark even if either the pulse voltage or the pulse frequency reaches the upper limit, it is preferable to increase the pulse voltage or pulse frequency that has not reached the upper limit in stages after a certain period of time has elapsed. .

In a preferred embodiment of the invention, the period of time is about 5 seconds. Further, when lowering the pulse voltage, the pulse voltage is lowered by 5 to 10%, and when increasing the pulse voltage, the pulse voltage is increased by 2 to 3%. Furthermore, when lowering the pulse frequency, the pulse frequency
When increasing the pulse frequency, increase the pulse voltage by 10-20%.

Effect In the pulse charging method, if the base voltage is appropriately controlled near the corona starting voltage, there are only two things to be controlled in order to suppress the generation of sparks: the pulse voltage and the pulse frequency. In the pulse charging method, if the base voltage is considered constant, the peak voltage is determined by the pulse voltage.

As mentioned above, the higher the pulse voltage, the better the dust collection performance, and when the pulse frequency exceeds a certain value, the pulse voltage cannot be maintained high due to sparks, but up to that value, the pulse frequency is high. It's better.

In this way, the pulse frequency and pulse voltage are
The spark generation area is shown in FIG. 2 on a plane. When a spark occurs, the electric charge stored between the discharge electrode and the dust collection electrode of the electrostatic precipitator is lost, the potential difference between the electrodes decreases, and the dust collection efficiency decreases significantly, so the non-spark area in Figure 2 , is the drivable area.

As can be seen from Figure 2, when the base voltage is properly controlled, the maximum pulse voltage that can be applied without sparking is constant regardless of the pulse frequency when the pulse frequency is low, but Once the pulse frequency is exceeded, it decreases as the pulse frequency increases. Therefore, when operating at the pulse frequency that is just before the maximum pulse voltage that can be applied without sparking begins to drop, as indicated by the circle in Figure 2, and when operating at the maximum pulse voltage at that time, the dust collection performance will be at its maximum. becomes. This is also confirmed by the specific data that will be presented later.

Therefore, maximum dust collection efficiency can be achieved by operating the pulse charging type electrostatic precipitator in the region indicated by the circle in FIG.

According to the method according to the features of the present invention, the pulse voltage and pulse frequency are changed little by little for a certain period of time, that is, for each stage, and the control method is changed depending on which stage a spark is generated. Note that within the same stage period, it does not matter whether the spark is "applying a pulse" or "applying a base voltage between pulses."

And when a spark occurs, the pulse voltage,
Reduce one or both of the pulse frequencies to prevent spark recurrence. When the spark-free period continues for a certain amount of time, the pulse voltage and pulse frequency are restored or increased, and eventually the pulse voltage and pulse frequency reach the area indicated by the circle in FIG. 2.

According to the method according to the feature of the present invention, even if the area of the circle in FIG.
The pulse voltage and pulse frequency can be applied to the marked area. Therefore, the operating state can be converged to the optimal pulse frequency and pulse voltage, and the maximum dust collection efficiency can be achieved.

Embodiment FIG. 3 is a block diagram showing an example of a power supply device for a pulse charging type electrostatic precipitator that implements the charge control method according to the present invention.

The illustrated power supply device for the electrostatic precipitator includes a pulse power source 6 and a base power source 8 connected to the discharge electrode of the electrostatic precipitator main body 9. The base power supply 8 may have any configuration as long as it controls the base voltage to an appropriate value (near the corona starting voltage).

The pulse power source 6 includes a step-up transformer 2 whose primary side is connected to a commercial AC power source via a thyristor gate circuit 1 consisting of a pair of thyristors connected in opposite directions, and a step-up transformer 2 on the secondary side of the step-up transformer. and a rectifying bridge 3 connected thereto.

The output terminal of the rectifying bridge 3 is connected to a pulse generating circuit 4. Furthermore, the output terminal of the rectifier bridge 3 is equipped with a
A pulse power measuring device 5 such as a voltage dividing resistor is connected, and its inverse output terminal is input to a control device 10 . On the other hand, the opposite output terminal of the rectifier bridge 3 is grounded.

The control device 10 issues a trigger signal to the pulse generation circuit 4, and the pulse generation circuit 4 outputs a pulse for each trigger signal. The output of the pulse generating circuit 4 is connected to the discharge electrode of the electrostatic precipitator main body 9, and the collecting electrode of the electrostatic precipitator main body 1 is grounded.

Furthermore, the discharge electrode of the electrostatic precipitator main body 9 is equipped with a device to monitor the electrostatic precipitator voltage and detect sparks.
A spark detection device 7, such as a voltage dividing resistor, is connected, and its output terminal is input to a control device 10.

The control device 10 is, for example, a computer, and is programmed to perform the operations described in detail below. Basically, the voltage from the pulse power measuring device 5 is compared with the target value set by the control device 10, and the firing angle of the thyristor of the thyristor gate circuit 1 is controlled to supply the voltage to the transformer 3. The power is controlled to provide feedback control of the pulse voltage to the target value. On the other hand, the control device 10 monitors the voltage detected by the spark detection device 7, and determines that a spark has occurred when a sudden drop in voltage is detected. In that case, as will be described later, if the pulse voltage is increased during a certain period before spark generation, the power supplied to the transformer 2 is reduced by controlling the firing angle of the thyristor gate circuit 1, and the pulse voltage is increased. Reduce voltage. However, if the pulse frequency is increased during a certain period before spark generation,
Similarly, the pulse voltage is lowered and the pulse generation circuit 4 is controlled to lower the pulse frequency.

Next, how to determine the pulse voltage and pulse frequency will be described with reference to FIG.

If there is no spark for a certain period of time (for example, 5 seconds), the control device 10 increases the pulse voltage or pulse frequency a little. Furthermore, if there is no spark for a certain period of time, the pulse voltage or pulse frequency is increased slightly.

If a spark occurs at the time shown in Figure 4, the pulse voltage should be reduced to a certain degree, for example 5 to 10%.
make low. If this spark occurred during a period immediately after increasing the pulse frequency, the pulse frequency should also be reduced by some degree, for example 30-50%.

After a spark, as described above, if there is no spark, the pulse voltage is increased little by little, for example, by 2 to 3%, at regular intervals, until it is slightly lower, for example, by 1 to 2%, than the pulse voltage at which the spark occurred last time. (as of Figure 4).

After the next fixed period has elapsed, the pulse frequency is increased at the time point in FIG. This increase is
The width should be 10-20% and smaller than the width that is reduced for each spark.

Even in this state, if sparks still do not occur, the spark is fired a predetermined number of times (for example, 2 to 4 times) at regular intervals.
times), the pulse voltage is increased while maintaining the increased pulse frequency. If no spark still occurs after that, the pulse frequency is increased once after a period of time. If no spark is generated yet, the pulse voltage is increased at regular intervals while maintaining the increased pulse frequency.

In this manner, the pulse voltage or pulse frequency is increased until a spark occurs (FIG. 4).

If the pulse voltage and pulse frequency are controlled in this way, when a spark occurs when the pulse frequency is lower than the optimum point, as at point A in Figure 5, the operating point will return to its original value, and then the pulse voltage will be adjusted again. Let it recover and increase the pulse frequency. When the spark occurs after that, as shown by the arrow in the figure, ′→
Repeat ′→′→′→″. In this way, the operating point approaches the optimal point marked with ○.In other words, only when increasing the pulse voltage, if a spark occurs, the pulse frequency gradually decreases. As the pulse voltage and pulse frequency continue to increase, an optimum point is reached.

On the other hand, when a spark occurs when the pulse frequency is higher than the optimum point, as at point A in FIG. 6, the pulse voltage is lowered to a point where the pulse voltage is lowered to a point where the pulse voltage is recovered to a point where the pulse voltage is restored to a point where the pulse voltage is lowered to a point where the pulse voltage is lowered to a point where the pulse voltage is lowered to a point where the pulse voltage is higher than the optimum point. If sparks occur when the pulse frequency is further increased, move to '' where both the pulse voltage and pulse frequency are decreased. Note that the pulse frequency when moving from to' is decreased by more than the increase in pulse frequency when moving from to.

After '' in FIG. 6, when the pulse voltage and pulse frequency are increased as '→'→', a spark occurs again at ''. Since the transition from ' to ' is an increase in the pulse voltage, only the pulse voltage is lowered and the pulse voltage shifts to '. Then, it is restored to '. Furthermore, if the pulse frequency is increased and a spark is generated, the

Claims (1)

[Claims] 1. In an electrostatic precipitator to which a DC base voltage and a pulse voltage are applied in a superimposed manner, if no spark is generated in the precipitator, either the pulse voltage or the pulse frequency is gradually reduced at regular intervals. When a spark occurs, lower the pulse voltage if the spark occurs after the pulse voltage has increased;
In addition, if the spark occurs after the pulse frequency has increased, the pulse voltage is lowered and the pulse frequency is decreased by a width greater than the pulse frequency increase width, and if no spark occurs thereafter, at regular intervals, first, the pulse where the previous spark occurred is Increase the pulse voltage step by step until the voltage is just below the voltage, then increase the pulse frequency step by step. If no spark occurs in the dust collector during that time, continue to increase the pulse voltage and pulse frequency at regular intervals. Charging control of a pulse charging type electrostatic precipitator, characterized in that either one is raised little by little, and on the other hand, when a spark is generated in the precipitator during that time, the above-mentioned operation at the time of spark generation is performed at the time when the spark is generated. Method. 2. When there is no spark even when either the pulse voltage or the pulse frequency reaches the upper limit, the pulse voltage or the pulse frequency that has not reached the upper limit is increased stepwise after a certain period of time. A charging control method for a pulse charging type electrostatic precipitator according to Scope 1. 3. The charging control method for a pulse charging type electrostatic precipitator according to claim 1 or 2, wherein the certain period is about 5 seconds. 4. Claims 1 to 3 are characterized in that when lowering the pulse voltage, the pulse voltage is lowered by 5 to 10%, and when increasing the pulse voltage, the pulse voltage is increased by 2 to 3%. A charging control method for a pulse charging type electrostatic precipitator according to any one of the items. 5 When lowering the pulse frequency, reduce the pulse frequency.
The pulse charging type electrostatic precipitator according to any one of claims 1 to 4, wherein the pulse voltage is lowered by 30 to 50%, and when the pulse frequency is increased, the pulse voltage is increased by 10 to 20%. charge control method.